It would be nice to not automatically start the promotion as soon as you buy it, so you can buy it first and then spend the rest of your money on other upgrades.
Good idea, thanks! I'll change it for the next update: buying the promotion no longer starts it. The button becomes a switch instead, so you can pay, spend what's left on upgrades, and start the challenge when you're ready (or switch it off and play a normal day first).
